In order for the scenario of a world devoid of plants and filled with towering skyscrapers to be possible, a new and sustainable source of energy for all life forms would need to be discovered. Photosynthesis and cellular respiration are the primary processes that power all life on Earth, including plants and humans alike.
Photosynthesis converts sunlight into organic compounds necessary for plant growth and cellular respiration releases energy from organic compounds to power biological processes. Without plants, there would be no source of organic compounds, and without cellular respiration, there would be no energy available for biological processes.
Therefore, a world without plants would require a completely different source of energy, such as synthetic materials or renewable energy sources such as wind or solar power, to power the skyscrapers and other technological advancements seen in these fictional depictions. However, these alternative energy sources would not be able to provide the organic compounds necessary for biological life and would have to be supplemented with other sources of nutrition and energy.
In conclusion, a world devoid of plants as depicted in many works of fiction is not possible based on our current understanding of the biosphere and energy flow in the ecosystem.